All helmets are tested towards standards. The result from that test is simply good/not good enough to qualify for use. There is very little data in the way of which helmets that are better than required.
The best helmet is one that you wear. MIPS and similar systems do offer some advantage, but only If it fits your head.
As someone that had an EXTREMELY bad concussion and have also written papers on the effects of helmets in crashes, let me say this - the standard foam plastic helmet is just about as good a nothing at all. And finally the industry is coming around to see that,
Bontrager (Trek) makes the Wave Cell helmet design to reduce fall over forces to those that are less than will cause a concussion.
I have just recently seen an article that Rudy has also gotten into the head protection rather than sell-em-a-cheap-plastic-gob. In my opinion it is far too early to say whether these helmets are real improvements but we can definitely say that they are an improvement over foam helmets.
There are two basic types of accidents: 1. You are traveling slowly and fall over for one reason or another. Helmet definitely help in these sorts of accidents if they do nothing more than prevent your head from being but or bruised.
2. You are hit by a car. These are EXTREMELY rare and in most cased you have multiple serious injuries like broken ribs etc which can be deadly. A helmet in this sort of accident is useless or nearly so.
Now certainly there are intermediate accidents such as descending at high speed and running into a tree head first. Or being accidently tipped over by a car passing too close and hitting you with a rear view mirror that can knock you off the bike. But these are EXTREMELY RARE.
So the accidents in which a helmet can make a difference is the falling over at a stop sign type. In these types that Bontrager and the Rudy if it is what they claim it is, are definitely improvements over the older foam helmets. If the color of the padding changes very much it is time for a new helmet since this can mean degradation of the padding.
I am now 77 and still riding and still climbing. The concussion I received was from the failure of a first generation carbon fiber fork. The fork had started to fail and was making noise so I bent down while riding to see what was causing the noise just as the fork collapsed. My head fell less than 3 feet and I was only going about 5 mph. I am now stuck with taking medication for the rest of my life that has some nasty side effects like being dizzy all the time and not being able to feel my feet. So it is well to try and avoid concussions.